udhcp源码剖析（五）——DHCP客户端重要的数据结构和初始化配置

来源：互联网发布：淘宝访客平均价值编辑：程序博客网时间：2024/06/04 17:43

数据结构

和服务器类似，客户端也维护着一个全局的数据结构client_config，用于所有的DHCP服务。

struct client_config_t client_config = {    /* Default options. */    abort_if_no_lease: 0,    foreground: 0,    quit_after_lease: 0,    background_if_no_lease: 0,    interface: "eth0",    pidfile: NULL,    script: DEFAULT_SCRIPT,    clientid: NULL,    hostname: NULL,    ifindex: 0,    arp: "\0\0\0\0\0\0",        /* appease gcc-3.0 */};

该结构在dhcpc.h中定义，并在dhcpc.c中设置默认值

struct client_config_t client_config = {    /* Default options. */    abort_if_no_lease: 0,    foreground: 0,    quit_after_lease: 0,    background_if_no_lease: 0,    interface: "eth0",    pidfile: NULL,    script: DEFAULT_SCRIPT,    clientid: NULL,    hostname: NULL,    ifindex: 0,    arp: "\0\0\0\0\0\0",        /* appease gcc-3.0 */};

其它全局变量

其余所需要的重要的全局变量都以简单数据结构给出，并没有专门设计复杂结构。

static int state;static unsigned long requested_ip; /* = 0，请求的IP */static unsigned long server_addr;       //服务器地址static unsigned long timeout;       //租约超时时刻    static int packet_num; /* = 0 */        //可认为是连续重复发送数据包的次数static int fd;                  //本地socket监听的fdstatic int signal_pipe[2];          //本地接收signal消息的pipe fd

udhcpc_main的初始化和配置

dhcpc的初始化和dhcpd类似，但是简化了很多操作，并且添加了对传入参数的解析和处理。

解析arg选项

对启动时传递的arg选项的解析，通过这些选项，DHCP可以选择多种模式运行，比如传递参数q，即设置quit_after_lease=1，客户端将在成功获得lease之后退出。

enum {        OPT_c = 1 << 0,        OPT_C = 1 << 1,        OPT_V = 1 << 2,        OPT_f = 1 << 3,        OPT_b = 1 << 4,        OPT_H = 1 << 5,        OPT_h = 1 << 6,        OPT_F = 1 << 7,        OPT_i = 1 << 8,        OPT_n = 1 << 9,        OPT_p = 1 << 10,        OPT_q = 1 << 11,        OPT_R = 1 << 12,        OPT_r = 1 << 13,        OPT_s = 1 << 14,        OPT_T = 1 << 15,        OPT_t = 1 << 16,        OPT_v = 1 << 17,        OPT_S = 1 << 18,    };#if ENABLE_GETOPT_LONG    static const char udhcpc_longopts[] ALIGN1 =        "clientid\0"      Required_argument "c"        "clientid-none\0" No_argument       "C"        "vendorclass\0"   Required_argument "V"        "foreground\0"    No_argument       "f"        "background\0"    No_argument       "b"        "hostname\0"      Required_argument "H"        "hostname\0"      Required_argument "h"        "fqdn\0"          Required_argument "F"        "interface\0"     Required_argument "i"        "now\0"           No_argument       "n"        "pidfile\0"       Required_argument "p"        "quit\0"          No_argument       "q"        "release\0"       No_argument       "R"        "request\0"       Required_argument "r"        "script\0"        Required_argument "s"        "timeout\0"       Required_argument "T"        "version\0"       No_argument       "v"        "retries\0"       Required_argument "t"        "syslog\0"        No_argument       "S"        ;#endif    /* Default options. */    client_config.interface = "eth0";    client_config.script = DEFAULT_SCRIPT;    client_config.retries = 3;    client_config.timeout = 3;    /* Parse command line */    opt_complementary = "c--C:C--c" // mutually exclusive                        ":hH:Hh"; // -h and -H are the same#if ENABLE_GETOPT_LONG    applet_long_options = udhcpc_longopts;#endif    opt = getopt32(argv, "c:CV:fbH:h:F:i:np:qRr:s:T:t:vS",        &str_c, &str_V, &str_h, &str_h, &str_F,        &client_config.interface, &client_config.pidfile, &str_r,        &client_config.script, &str_T, &str_t        );    if (opt & OPT_c)        client_config.clientid = alloc_dhcp_option(DHCP_CLIENT_ID, str_c, 0);    //if (opt & OPT_C)    if (opt & OPT_V)        client_config.vendorclass = alloc_dhcp_option(DHCP_VENDOR, str_V, 0);    if (opt & OPT_f)        client_config.foreground = 1;    if (opt & OPT_b)        client_config.background_if_no_lease = 1;    if (opt & OPT_h)        client_config.hostname = alloc_dhcp_option(DHCP_HOST_NAME, str_h, 0);    if (opt & OPT_F) {        client_config.fqdn = alloc_dhcp_option(DHCP_FQDN, str_F, 3);        /* Flags: 0000NEOS        S: 1 => Client requests Server to update A RR in DNS as well as PTR        O: 1 => Server indicates to client that DNS has been updated regardless        E: 1 => Name data is DNS format, i.e. <4>host<6>domain<4>com<0> not "host.domain.com"        N: 1 => Client requests Server to not update DNS        */        client_config.fqdn[OPT_DATA + 0] = 0x1;        /* client_config.fqdn[OPT_DATA + 1] = 0; - redundant */        /* client_config.fqdn[OPT_DATA + 2] = 0; - redundant */    }    // if (opt & OPT_i) client_config.interface = ...    if (opt & OPT_n)        client_config.abort_if_no_lease = 1;    // if (opt & OPT_p) client_config.pidfile = ...    if (opt & OPT_q)        client_config.quit_after_lease = 1;    if (opt & OPT_R)        client_config.release_on_quit = 1;    if (opt & OPT_r)        requested_ip = inet_addr(str_r);    // if (opt & OPT_s) client_config.script = ...    if (opt & OPT_T)        client_config.timeout = xatoi_u(str_T);    if (opt & OPT_t)        client_config.retries = xatoi_u(str_t);    if (opt & OPT_v) {        printf("version %s\n", BB_VER);        return 0;    }    if (opt & OPT_S) {        openlog(applet_name, LOG_PID, LOG_LOCAL0);        logmode |= LOGMODE_SYSLOG;    }

读取接口信息和设置信号处理器

这一步和服务器的基本一致，注意这里的不同是对clientid的初始化，以及run_script。

    if (read_interface(client_config.interface, &client_config.ifindex,               NULL, client_config.arp))        return 1;    /* Make sure fd 0,1,2 are open */    bb_sanitize_stdio();    /* Equivalent of doing a fflush after every \n */    setlinebuf(stdout);    /* Create pidfile */    write_pidfile(client_config.pidfile);    /* if (!..) bb_perror_msg("cannot create pidfile %s", pidfile); */    /* Goes to stdout and possibly syslog */    bb_info_msg("%s (v%s) started", applet_name, BB_VER);    /* if not set, and not suppressed, setup the default client ID */    if (!client_config.clientid && !(opt & OPT_C)) {        client_config.clientid = alloc_dhcp_option(DHCP_CLIENT_ID, "", 7);        client_config.clientid[OPT_DATA] = 1;        memcpy(client_config.clientid + OPT_DATA+1, client_config.arp, 6);    }    if (!client_config.vendorclass)        client_config.vendorclass = alloc_dhcp_option(DHCP_VENDOR, "udhcp "BB_VER, 0);    /* setup the signal pipe */    udhcp_sp_setup();    state = INIT_SELECTING;    udhcp_run_script(NULL, "deconfig");    change_mode(LISTEN_RAW);    tv.tv_sec = 0;    goto jump_in;

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